Search results for "Photocatalysis."

Structural and surface characterization of the polycrystalline system CrxOy · TiO2 employed for photoreduction of dinitrogen and photodegradation of …

1992

The polycrystalline system CrxOy-TiO2, used as a catalyst for photoreactions, was studied by X-ray diffractometric method, visible-ultraviolet diffuse reflectance and infrared spectroscopic methods, surface area determination, and porosimetry to characterize its structural and surface features. Two series of catalysts were prepared by two different methods, namely by coprecipitation and by impregnation. The first series was tested as photocatalysts for the dinitrogen photoreduction in a gas-solid regime and for the phenol photodegradation in a liquid-solid regime. The results indicate that the interaction of chromium ions with OH groups modifies the surface properties of the supports and co…

Membranes for photocatalysis in water and wastewater treatment

2011

Abstract: The chapter reports the basic principles of heterogeneous photocatalysis together with a brief presentation of the types of membranes and membrane operations most widely used in this type of application. Coupling the two technologies with the aim of obtaining synergistic effects for conversion in liquid–solid systems is discussed and the relevant papers together with some case studies in pollutants abatement and reaction of synthesis are highlighted.

Cyanuric Acid Oxidationi in UV Irradiated ZnO Suspensions

2008

Preparation of photocatalytic brookite thin films

2007

Pure brookite films were deposited from a brookite dispersion obtained by peptizing a mixture brookite–rutile prepared by thermolysis of TiCl4 in a HCl solution. The films were characterised by X-ray diffraction and Raman spectroscopy. The photoactivity of the samples was tested by using the photo-oxidation of 2-propanol in gas–solid regime as a probe reaction. The brookite films efficiently degraded 2-propanol under UV illumination.

Inorganic gels as precursors of TiO2 photocatalysts prepared by low temperature microwave or thermal treatment

2008

Abstract A simple procedure for preparing active TiO2 photocatalysts is presented. The starting materials were unusual TiO2 gels formed from TiCl4. The use of microwaves for a very short time enhanced the TiO2 crystallinity preventing an increase of particle size and minimizing the decrease of specific surface area. This result makes this preparation very attractive. The formation of the gels was monitored through measurements of viscosity. All the samples were characterized by means of X-ray diffraction, diffuse reflectance spectroscopy and BET specific surface area measurements. The photoactivity of the samples was evaluated using the photodegradation of 4-nitrophenol in liquid–solid regi…

Sol-gel synthesis and photocatalytic activity of ZnO-SnO2 nanocomposites

2014

Abstract ZnO–SnO 2 nanocomposites were synthesized by a facile sol–gel synthesis route and characterized through X-ray diffraction, BET specific surface area analysis, UV–vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy. The photocatalytic activity of the samples was tested using the degradation of 4-nitrophenol under UV light as model reaction. The ZnO/SnO 2 molar ratio was varied in order to study its influence on the photoefficiency of the samples. The ZnO–SnO 2 nanocomposites showed higher photoactivity than the pure oxides and in particular the sample with ZnO/SnO 2 mol…

Photocatalytic behaviour of metal-loaded TiO2 aqueous dispersions and films

2007

Abstract Titanium dioxide nanoparticles loaded with Ce, Co, Eu, Sm, W and Yb species were prepared by coprecipitation in mild conditions using TiCl 4 as precursor with the aim to enhance the photocatalytic activity, especially under visible light irradiation. The photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (SSA) determination and UV–Vis diffuse reflectance spectroscopy. The photocatalytic activity of the powders of pure and loaded TiO 2 was investigated by employing the photodegradation of 4-nitrophenol as probe reaction in a liquid–solid system. Loading with suitable amounts of W, Co and Sm resulted in a significan…

Coupled Semiconductor Systems for Photocatalysis. Preparation and Characterization of Polycrystalline Mixed WO3/WS2 Powders

1999

Mixed WO3/WS2 powders were prepared by oxidation of WS2. The physical properties of the samples were characterized by X-ray diffraction, diffuse reflectance spectroscopy, and scanning electron microscopy; they were strongly dependent upon the time and temperature of oxidation. The chemical state and the elemental distribution of the sample surface were investigated by X-ray photoelectron spectroscopy. The photocatalytic results have showed that the aqueous suspensions of the mixed WO3/WS2 systems have significantly higher activities than pure WS2 and WO3 for the photodegradation of phenol. The enhanced performance can be related to the presence of heterojunctions WO3/WS2 on the single parti…

Electro- and Photo-driven Reduction of CO 2 by a trans -(Cl)-[Os(diimine)(CO) 2 Cl 2 ] Precursor Catalyst: Influence of the Diimine Substituent and A…

2016

A series of [OsII(NN)(CO)2Cl2] complexes where NN is a 2,2′-bipyridine ligand substituted in the 4,4′ positions by H (C1), CH3 (C2), C(CH3)3 (C3), or C(O)OCH(CH3)2 (C4) has been studied as catalysts for the reduction of CO2. Electrocatalysis shows that the selectivity of the reaction can be switched toward the production of CO or HCOO− with an electron-donating (C2, C3) or -withdrawing (C4) substituent, respectively. The electrocatalytic process is a result of the formation of an Os0-bonded polymer, which was characterized by electrochemistry, UV/Visible and EPR spectroscopies. Photolysis of the complexes under CO2 in DMF+TEOA produces CO as a major product with a remarkably stable turnover…

The Existence of Nitrate Radicals in Irradiated TiO 2 Aqueous Suspensions in the Presence of Nitrate Ions

2018

Evidence of the existence of nitrate radical in irradiated aqueous TiO2 suspensions in the presence of nitrate ions are reported for the first time. The joint use of UV/Vis and EPR spectroscopy showed that nitrate radicals are formed by hole induced oxidation of nitrate ions. Photocatalytic degradation of a model alkene compound allowed to highlight the presence of an intermediate organic nitrate deriving from nitrate radical attack to the double bond of the substrate. These results not only allow deeper understanding of photocatalytic processes, but open the route to new green photocatalytic syntheses initiated by nitrate radicals and to new insights in the field of atmospheric chemistry.